Scalable encapsulation of hepatocytes by electrostatic spraying

Polymer microcapsules and microbeads as cell carriers for in vivo biomedical applications

Polymer microcarriers are being extensively explored as cell delivery vehicles in cell-based therapies and hybrid tissue and organ engineering. Spherical microcarriers are of particular interest due to easy fabrication and injectability. They include microbeads, composed of a porous matrix, and microcapsules, where matrix core is additionally covered with a semipermeable membrane. Microcarriers provide cell containment at implantation site and protect the cells from host immunoresponse, degradation and shear stress. Immobilized cells may be genetically altered to release a specific therapeutic product directly at the target site, eliminating side effects of systemic therapies. Cell microcarriers need to fulfil a number of extremely high standards regarding their biocompatibility, cytocompatibility, immunoisolating capacity, transport, mechanical and chemical properties. To obtain cell microcarriers of specified parameters, a wide variety of polymers, both natural and synthetic, and immobilization methods can be applied. Yet so far, only a few approaches based on cell-laden microcarriers have reached clinical trials. The main issue that still impedes progress of these systems towards clinical application is limited cell survival in vivo. Herein, we review polymer biomaterials and methods used for fabrication of cell microcarriers for in vivo biomedical applications. We describe their key limitations and modifications aiming at improvement of microcarrier in vivo performance. We also present the main applications of polymer cell microcarriers in regenerative medicine, pancreatic islet and hepatocyte transplantation and in the treatment of cancer. Lastly, we outline the main challenges in cell microimmobilization for biomedical purposes, the strategies to overcome these issues and potential future improvements in this area.

Collagen-Based Microcapsules As Therapeutic Materials for Stem Cell Therapies in Infarcted Myocardium

As cell therapies emerged, it was quickly realized that pro-regenerative cells directly injected into injured tissue struggled within the inflammatory microenvironment. By using microencapsulation, i.e., encapsulating cells within polymeric biomaterials, they are henceforth protected from the harmful extracellular cues, while still being able to receive oxygen and nutrients and release secreted factors. Previous work showed that stem cells encapsulated within a biologically inert material (agarose) were able to significantly improve the function of the infarcted mouse heart. With the aim of using more bioresponsive microcapsules, we sought to develop an enzymatically degradable, type I collagen-based microcapsule for the intramyocardial delivery of bone marrow-derived mesenchymal stromal cells in a murine model of myocardial infarction.

Mesenchymal stem cell 3D encapsulation technologies for biomimetic microenvironment in tissue regeneration

Mesenchymal stem cell (MSC) encapsulation technique has long been emerged in tissue engineering as it plays an important role in implantation of stem cells to regenerate a damaged tissue. MSC encapsulation provides a mimic of a three-dimensional (3D) in vivo environment to maintain cell viability and to induce the stem cell differentiation which regulates MSC fate into multi-lineages. Moreover, the 3D matrix surrounding MSCs protects them from the human innate immune system and allows the diffusion of biomolecules such as oxygen, cytokines, and growth factors. Therefore, many technologies are being developed to create MSC encapsulation platforms with diverse materials, shapes, and sizes. The conditions of the platform are determined by the targeted tissue and translation method. This review introduces several details of MSC encapsulation technologies such as micromolding, electrostatic droplet extrusion, microfluidics, and bioprinting and their application for tissue regeneration. Lastly, some of the challenges and future direction of MSC encapsulation technologies as a cell therapy-based tissue regeneration method will be discussed.

Living Cell Factories - Electrosprayed Microcapsules and Microcarriers for Minimally Invasive Delivery

Minimally invasive delivery of "living cell factories" consisting of cells and therapeutic agents has gained wide attention for next generation biomaterial device systems for multiple applications including musculoskeletal tissue regeneration, diabetes and cancer. Cellular-based microcapsules and microcarrier systems offer several attractive features for this particular purpose. One such technology capable of generating these types of systems is electrohydrodynamic (EHD) spraying. Depending on various parameters, including applied voltage, biomaterial properties (viscosity, conductivity) and needle geometry, complex structures and arrangements can be fabricated for therapeutic strategies. The advances in the use of EHD technology are outlined, specifically in the manipulation of bioactive and dynamic material systems to control size, composition and configuration in the development of minimally invasive micro-scaled biopolymeric systems. The exciting therapeutic applications of this technology, future perspectives and associated challenges are also presented.

Rapid large-scale culturing of microencapsulated hepatocytes: a promising approach for cell-based hepatic support

INTRODUCTION

The efficacy of any bioartificial liver device requires both rapid production and proper bioactivity of the cells for the bioreactor. The goal of this study was to observe the effect of spinner speed and cell density on the proliferation of microencapsulated immortalized human hepatocytes (HepLL) and human hepatoma (HepG2) cells.

MATERIALS AND METHODS

Alginate-chitosan microcapsulated HepG2 and HepLL cells were randomly divided into 2 groups, and each group was further divided into 8 subgroups according to embedded cell density and spinner speed. The growth, metabolism, and functions of the encapsulated cells in each group were evaluated.

RESULTS

In each group, the cell number, ammonium removal, albumin synthesis, and diazepam clearance increased significantly with the spinner speed, whereas embedded cell density had no impact. Albumin synthesis, removal of ammonium, and diazepam clearance were significantly higher in the microencapsulated HepLL groups than in HepG2 cells at any time point, without any significant difference in cell numbers.

CONCLUSIONS

Spinner culture significantly promoted microencapsulated HepLL and HepG2 cell bioactivity. Wrapped cells had optimal function on day 10 in rolling culture groups. These data show that HepLL cells would be a promising candidate for cell-based liver support therapy.

Preparation of methotrexate-loaded, large, highly-porous PLLA microspheres by a high-voltage electrostatic antisolvent process

A high-voltage (10 kV) electrostatic antisolvent process was used to prepare methotrexate (MTX)-loaded, large, highly-porous poly-L-lactide (PLLA) microspheres. MTX solution in dimethyl sulfoxide (DMSO) and PLLA solution in dichloromethane (DCM) were homogeneously mixed, and then ammonium bicarbonate (AB) aqueous solution was added. The mixed solution was emulsified by ultrasonication with Pluronic F127 (PF127) as an emulsion stabilizer. The emulsion was electrosprayed by the specific high-voltage apparatus and dropped into a 100 mL of ethanol, which acted as an antisolvent for the solute and extracted DMSO and DCM, causing the co-precipitation of PLLA and MTX, thus forming microspheres with AB aqueous micro-droplets uniformly inlaid. The obtained MTX-PLLA microspheres were subsequently lyophilized to obtain large, highly-porous MTX-PLLA microspheres, which exhibited an identifiable spherical shape and a rough surface furnished with open pores, with a mean particle size of 25.0 μm, mass median aerodynamic diameter of 3.1 ± 0.2 μm, fine-particle fraction of 57.1 ± 1.6 %, and porosity of 81.8 %; furthermore, they offered a sustained release of MTX. X-ray diffraction and Fourier transform-infrared spectra revealed that no crystallinity or alteration of chemical structure occurred during the high-voltage electrostatic antisolvent process, which in this study was proved to have great potential for preparing highly-porous drug-loaded polymer microspheres for use in pulmonary drug delivery.

Combining submerged electrospray and UV photopolymerization for production of synthetic hydrogel microspheres for cell encapsulation

Microencapsulation within hydrogel microspheres holds much promise for drug and cell delivery applications. Synthetic hydrogels have many advantages over more commonly used natural materials such as alginate, however their use has been limited due to a lack of appropriate methods for manufacturing these microspheres under conditions compatible with sensitive proteins or cells. This study investigated the effect of flow rate and voltage on size and uniformity of the hydrogel microspheres produced via submerged electrospray combined with UV photopolymerization. In addition, the mechanical properties and cell survival within microspheres was studied. A poly(vinyl alcohol) (PVA) macromer solution was sprayed in sunflower oil under flow rates between 1-100 µL/min and voltages 0-10 kV. The modes of spraying observed were similar to those previously reported for electrospraying in air. Spheres produced were smaller for lower flow rates and higher voltages and mean size could be tailored from 50 to 1,500 µm. The microspheres exhibited a smooth, spherical morphology, did not aggregate and the compressive modulus of the spheres (350 kPa) was equivalent to bulk PVA (312 kPa). Finally, L929 fibroblasts were encapsulated within PVA microspheres and showed viability >90% after 24 h. This process shows great promise for the production of synthetic hydrogel microspheres, and specifically supports encapsulation of cells.

Encapsulation of Neural Cells in Nano-Featured Polymer Scaffolds through Co-axial Electrospinning

Encapsulation of PC12 cells (neural cell model) in alginate hydrogels with a protective coating of poly(lactic-co-glycolic acid) (PLGA) was achieved in the present study using co-axial electrospinning. Co-axial electrospinning consists of two concentric capillaries compared to only one capillary in conventional electrospinning. This allows for the processing of two liquid solutions simultaneously. Neural cells suspended in hydrogels were injected in the inner capillary, while the carbon nanotubes (added for conductivity) suspended in PLGA were injected in the outer capillary at controlled flow rates. On the application of a high voltage, a compound jet formed at the capillary exits and resulted in a co-electrospun fiber of nerve cells encapsulated in PLGA with carbon nanotubes. Carbon nanotubes were included to make the outer shell conductive to stimulate the PC12 cells. In this study, the voltage varied from 0 to 15 kV and various flow rates were tested to achieve a stable cone-jet mode in electrospinning. The cell density in the media varied from 0.5 to5 million cells/ml and the polymer solution (PLGA) concentration varied from 1 to 10 mg/ml. This resulted in a three dimensional conductive scaffold with nano-features (due to carbon nanotubes) on the polymer surface, which were collected on the grounded substrate. PC12 cells were found to be viable inside microspheres after 3 days. The size of the microspheres was quite uniform and less than 200 μm. This technique may be very useful for the development of cell encapsulated scaffolds which mimic natural body tissue organization for tissue engineering applications such as nervous system regeneration.

Enhanced adsorption of arsenate onto a natural polymer-based sorbent by surface atom transfer radical polymerization

Arsenic contamination in water, especially in groundwater, has been recognized as an important issue of concern because of its high mobility and toxicity. In this study, N-methylglucamine was immobilized onto crosslinked chitosan beads via atom transfer radical polymerization for an efficient adsorption of arsenic. It was demonstrated that the immobilization significantly enhanced the adsorption capacity. The uptake onto the adsorbent was highly pH dependent, and a maximum adsorption capacity as high as 69.28 mg/g was obtained at the optimum pH of 5. Most of arsenate was rapidly adsorbed in the first 5h, and the adsorption equilibrium was established in 16 h, which was well described by an intraparticle diffusion model. The adsorbent exhibited a great uptake of the humic acid, which led to a decrease in the adsorption of arsenate. The effects of competitive anions on the adsorption exhibited the following descending sequence: sulfate ≫ phosphate>fluoride (negligible effect). Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that the arsenic adsorption resulted from the presence of tertiary amine and hydroxyl functional groups grafted on the crosslinked chitosan.

In vitro large-scale cultivation and evaluation of microencapsulated immortalized human hepatocytes (HepLL) in roller bottles

BACKGROUND/AIMS

Microencapsulated hepatocytes have been proposed as promising bioactive agents for packed-bed or fluidized-bed bioartificial liver assist devices (BLaDs) and for hepatocyte transplantation because of the potential advantages they offer of high mass transport rate and an optimal microenvironment for hepatocyte culture. We developed a large-scale and high-production alginate-chitosan (AC) microcapsule roller bottle culture system for the encapsulation of hepLL immortalized human hepatocytes. In this study, the efficacy of upscaling encapsulated hepLL cells production with roller bottle cultivation was evaluated in vitro.

METHODS

Microencapsulated hepLL cells were grown at high yield in large-scale roller bottles, with free cells cultured in roller bottle spinners serving as controls. The mechanical stability and the permeability of the AC microcapsules were investigated, and the growth, metabolism and functions of the encapsulated hepLL cells were evaluated as compared to free cells.

RESULTS

The microcapsules withstood well the shear stress induced by high agitation rates. The microcapsules were permeable to albumin, but prevented the release of immunoglobulins. Culture in roller bottles of immortalized human hepatocytes immobilized in the AC microcapsules improved cell growth, albumin synthesis, ammonia elimination and lidocaine clearance as compared with free cells cultured in roller bottles.

CONCLUSIONS

Encapsulated hepLL cells may be cultured on a large scale in roller bottles. This makes them possible candidates for use in cell-based liver assist therapies.

Encapsulation of Living Cells in Small (∼100 μm) Alginate Microcapsules by Electrostatic Spraying: A Parametric Study

A parametric study was performed to understand the effect of preparation parameters on size, morphology, and encapsulation efficiency (i.e., cells/microcapsule) of alginate microcapsules prepared using the electrostatic spray method. The preparation parameters studied include sodium alginate concentration, spray voltage, flow rate, and cell density. It was found that both the flow rate and spray voltage have a significant impact on microcapsule size while the microcapsule morphology is greatly influenced by both the sodium alginate concentration and spray voltage. To obtain small (∼100 μm) cell-loaded microcapsules with good morphology (i.e., round in shape and uniform in size) and high encapsulation efficiency (>5 cells/microcapsule), the optimal ranges of spray voltage, flow rate, alginate concentration, and cell density are from 1.6–1.8 kV, 1.5–3 ml/h, >1.5% (w/v), and (3–5)×106 cells/ml, respectively. Under optimal preparation conditions, cells were found to survive the microencapsulation process well.

Dispensing of very low volumes of ultra high viscosity alginate gels: a new tool for encapsulation of adherent cells and rapid prototyping of scaffolds and implants

We present a tool for dispensing very low volumes (20 nL or more) of ultra high viscosity (UHV) medical-grade alginate hydrogels. It uses a modified piezo-driven micrometering valve, integrated into a versatile system that allows fast prototyping of encapsulation procedures and scaffold production. Valves show excellent dispensing properties for UHV alginate in concentrations of 0.4% and 0.7% and also for aqueous liquids. An optimized process flow provides excellent handling of biological samples under sterile conditions. This technique allows the encapsulation of adherent cells and structuring of substrates for biotechnology and regenerative medicine. A variety of cell lines showed at least 70% viability after encapsulation (including cell lines that are relevant in regenerative medicine like Hep G2), and time-lapse analysis revealed cells proliferating and showing limited motility under alginate spots. Cells show metabolic activity, gene product expression, and physiological function. Encapsulated cells have contact with the substrate and can exchange metabolites while being isolated from macromolecules in the environment. Contactless dispensing allows structuring of substrates with alginate, isolation and transfer of cell-alginate complexes, and the dispensing of biological active hydrogels like extracellular matrix-derived gels.

Electrospray in the dripping mode for cell microencapsulation

Entrapment of living cells in microbeads is to protect the encapsulated cells from the host's immune system, which can be used as drug delivery vehicles, immunotherapies and engineered tissues. The main objective of the present study was to investigate the droplet formation and to better develop mono-dispersed microencapsulation of living cells with controllable size. The uniformity of microencapsulation size was realized by performing electrospray in the dripping mode and also stabilized by an additional ring electrode. Reduction of droplet diameter and increase in the dripping frequency were observed with increasing applied voltage to the nozzle using a conventional electrospray setup. The vibration of the needle was found to reduce when high voltage was applied to the nozzle. With increasing voltage applied to the ring electrode, the dripping frequency was found to decrease with the formation of slightly larger sizes of droplets. Hep G2 cell line was taken as the model cell line for encapsulation in calcium alginate microbeads. Relatively uniform microbeads could be achieved when operating under low flow rates with high voltages applied to the nozzle by using a conventional electrospray setup. In contrast, uniform microbeads can not be obtained using a similar setup under high flow rates unless the ring electrode is applied with voltage to stabilize the electrospray in the dripping mode. In this modified electrospray, microbeads with narrow size distribution and slightly larger size can be obtained even for cases under high flow rates. Phase contrast microscope images showed that the diameter of microbeads from around 200 microm to 2 mm could be finely tuned by adjusting various operating parameters.